Metamaterials are artificial materials that are engineered to have properties that are not found in nature, and that are not necessarily possessed by their constituent parts alone. In this sense, metamaterials may be assemblies of multiple individual elements, unit cells, or a cell array, on any scale, from nano to bulk.
A metamaterial simultaneously exhibiting a relative effective permeability and a relative effective permittivity below zero over a wide bandwidth, and may include: one of a two- or three-dimensional arrangement of unit cells or a cell array, each of the unit cells having a magnetic dipole moment and an electric dipole moment that are dependent upon one or more of an incident magnetic/electric field, and a coupling mechanism for coupling the incident magnetic field and electric field to one or more devices. Optionally, the coupling mechanism includes one or more of a split ring and a pair of parallel plates coupled by one of a rod and a wire.
Some artificial composite materials exhibit simultaneous negative values of electric permittivity (∈<0) and magnetic permeability (μ<0). These materials may exhibit the following properties: an artificial homogenous structure; simultaneous negative permittivity (−∈) and permeability (−μ); the electric field, magnetic field, and wave-vector of an electromagnetic wave therein forming a left-handed triad, and having backward wave propagation, anti-parallel group and phase velocity; reversal of Snell's Law (negative index of refraction); reversal of the Doppler effect; reversal of the Vavilov-Cerenkov effect; and breaking the diffraction-limit.
The characteristics of artificial composite metamaterials can depend on any of the properties of the host material, embedded material, the volume of the fraction, the operating frequency, and/or morphology of the composite material (e.g., dimension, shape of the host structure and/or guest structure). Thus, controlling the dynamics of the morphology of the embedded structure provides one way of control over a change of the properties of the artificial composite metamaterials (e.g., permittivity, permeability, refractive index).
One key to the design of artificial metamaterial resonators is selecting a geometric shape that induces currents that form loops with a relatively uniform distribution, thereby producing a strong magnetic moment. One type of geometry used is a split-ring resonator (SRR). SRRs are sub-wavelength resonators that are able to inhibit signal propagation in a narrow band within the vicinity of their resonant frequency, provided that the magnetic field is polarized along the ring's axis. SRRs can be modeled as LC resonant tanks that can be externally driven by a magnetic field to inhibit signal propagation in a narrow band if properly oriented. The particular resonance frequency or frequencies of a given medium having an SRR may depend on a combination of factors, including (a) width of the split or “break” of the ring, (b) ring width, (c) distance between concentric rings, (d) substrate permittivity, (e) substrate thickness, and (f) orientation of the SRR. Other factors may include the number of rings (e.g., 1, 2, 4, etc.) and the number of splits or breaks in each ring (e.g., 1, 2, 4, etc.) of the SRR. Factors like the width of the split, ring width, distance between concentric rings, and number of splits or breaks in each ring typically have a direct proportion with the resonant frequencies while factors like the substrate permittivity, substrate thickness typically have an inverse proportion to the resonant frequency.
It is known that tunable metamaterial ring resonators may be formed on a thin film. However, such tunable resonators generally act as their own medium and not, e.g., as a complementary circuit on a circuit board having another device (e.g., a voltage controlled oscillator). Moreover, known SRRs are generally configured to resonate at a frequency on the order of THz due to physical limitations in the shape and size of the SRR ring structure. Accordingly, and in order to implement an SRR structure as a complementary circuit on a circuit board, it would be desirable to provide an SRR cell and/or SRR array having a structure with physical parameters for improved performance.